Most of the Spanish examples cited by James Fidelholtz have a sequence
in hiatus in my dialect (Castilian): brioso [bri.o.so], frialdad
[fri.al.dad], criar [kri.ar], cliente [kli.en.te]. These sequences
contrast with the diphthong of other words such as pliegue [plje.ge],
Santiago [san.tja.go], etc. I believe these facts also hold for
Mexican Spanish, but not for all Latin American dialects. Non-native
speakers, no matter how fluent, are usually completely unaware of this
distinction, which is not made in the orthography. Dictionaries also
typically fail to record this phonemic distinction. But native
phoneticians such as Navarro Tomas, Quilis and Monroy Casas do report
this contrast and so does the grammar of the Spanish Academy.
Jose Ignacio Hualde
Dept. of Spanish, Italian, and Portuguese
4080 FLB
Univ. of Illinois, Urbana, IL 61801
j-hualdeuiuc.edu